/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package peasy.org.apache.commons.math.geometry;

import java.io.Serializable;

/**
 * This class implements vectors in a three-dimensional space.
 * <p>
 * Instance of this class are guaranteed to be immutable.
 * </p>
 * 
 * @version $Revision: 627998 $ $Date: 2008-02-15 03:24:50 -0700 (Fri, 15 Feb
 *          2008) $
 * @since 1.2
 */

public class Vector3D implements Serializable {

	/** First canonical vector (coordinates: 1, 0, 0). */
	public static final Vector3D plusI = new Vector3D(1, 0, 0);

	/** Opposite of the first canonical vector (coordinates: -1, 0, 0). */
	public static final Vector3D minusI = new Vector3D(-1, 0, 0);

	/** Second canonical vector (coordinates: 0, 1, 0). */
	public static final Vector3D plusJ = new Vector3D(0, 1, 0);

	/** Opposite of the second canonical vector (coordinates: 0, -1, 0). */
	public static final Vector3D minusJ = new Vector3D(0, -1, 0);

	/** Third canonical vector (coordinates: 0, 0, 1). */
	public static final Vector3D plusK = new Vector3D(0, 0, 1);

	/** Opposite of the third canonical vector (coordinates: 0, 0, -1). */
	public static final Vector3D minusK = new Vector3D(0, 0, -1);

	/** Null vector (coordinates: 0, 0, 0). */
	public static final Vector3D zero = new Vector3D(0, 0, 0);

	/**
	 * Simple constructor. Build a null vector.
	 */
	public Vector3D() {
		x = 0;
		y = 0;
		z = 0;
	}

	/**
	 * Simple constructor. Build a vector from its coordinates
	 * 
	 * @param x
	 *            abscissa
	 * @param y
	 *            ordinate
	 * @param z
	 *            height
	 * @see #getX()
	 * @see #getY()
	 * @see #getZ()
	 */
	public Vector3D(final double x, final double y, final double z) {
		this.x = x;
		this.y = y;
		this.z = z;
	}

	/**
	 * Simple constructor. Build a vector from its azimuthal coordinates
	 * 
	 * @param alpha
	 *            azimuth (&alpha;) around Z (0 is +X, &pi;/2 is +Y, &pi; is -X
	 *            and 3&pi;/2 is -Y)
	 * @param delta
	 *            elevation (&delta;) above (XY) plane, from -&pi;/2 to +&pi;/2
	 * @see #getAlpha()
	 * @see #getDelta()
	 */
	public Vector3D(final double alpha, final double delta) {
		final double cosDelta = Math.cos(delta);
		this.x = Math.cos(alpha) * cosDelta;
		this.y = Math.sin(alpha) * cosDelta;
		this.z = Math.sin(delta);
	}

	/**
	 * Multiplicative constructor Build a vector from another one and a scale
	 * factor. The vector built will be a * u
	 * 
	 * @param a
	 *            scale factor
	 * @param u
	 *            base (unscaled) vector
	 */
	public Vector3D(final double a, final Vector3D u) {
		this.x = a * u.x;
		this.y = a * u.y;
		this.z = a * u.z;
	}

	/**
	 * Linear constructor Build a vector from two other ones and corresponding
	 * scale factors. The vector built will be a1 * u1 + a2 * u2
	 * 
	 * @param a1
	 *            first scale factor
	 * @param u1
	 *            first base (unscaled) vector
	 * @param a2
	 *            second scale factor
	 * @param u2
	 *            second base (unscaled) vector
	 */
	public Vector3D(final double a1, final Vector3D u1, final double a2, final Vector3D u2) {
		this.x = a1 * u1.x + a2 * u2.x;
		this.y = a1 * u1.y + a2 * u2.y;
		this.z = a1 * u1.z + a2 * u2.z;
	}

	/**
	 * Linear constructor Build a vector from three other ones and corresponding
	 * scale factors. The vector built will be a1 * u1 + a2 * u2 + a3 * u3
	 * 
	 * @param a1
	 *            first scale factor
	 * @param u1
	 *            first base (unscaled) vector
	 * @param a2
	 *            second scale factor
	 * @param u2
	 *            second base (unscaled) vector
	 * @param a3
	 *            third scale factor
	 * @param u3
	 *            third base (unscaled) vector
	 */
	public Vector3D(final double a1, final Vector3D u1, final double a2,
			final Vector3D u2, final double a3, final Vector3D u3) {
		this.x = a1 * u1.x + a2 * u2.x + a3 * u3.x;
		this.y = a1 * u1.y + a2 * u2.y + a3 * u3.y;
		this.z = a1 * u1.z + a2 * u2.z + a3 * u3.z;
	}

	/**
	 * Linear constructor Build a vector from four other ones and corresponding
	 * scale factors. The vector built will be a1 * u1 + a2 * u2 + a3 * u3 + a4
	 * * u4
	 * 
	 * @param a1
	 *            first scale factor
	 * @param u1
	 *            first base (unscaled) vector
	 * @param a2
	 *            second scale factor
	 * @param u2
	 *            second base (unscaled) vector
	 * @param a3
	 *            third scale factor
	 * @param u3
	 *            third base (unscaled) vector
	 * @param a4
	 *            fourth scale factor
	 * @param u4
	 *            fourth base (unscaled) vector
	 */
	public Vector3D(final double a1, final Vector3D u1, final double a2,
			final Vector3D u2, final double a3, final Vector3D u3, final double a4,
			final Vector3D u4) {
		this.x = a1 * u1.x + a2 * u2.x + a3 * u3.x + a4 * u4.x;
		this.y = a1 * u1.y + a2 * u2.y + a3 * u3.y + a4 * u4.y;
		this.z = a1 * u1.z + a2 * u2.z + a3 * u3.z + a4 * u4.z;
	}

	/**
	 * Get the abscissa of the vector.
	 * 
	 * @return abscissa of the vector
	 * @see #Vector3D(double, double, double)
	 */
	public double getX() {
		return x;
	}

	/**
	 * Get the ordinate of the vector.
	 * 
	 * @return ordinate of the vector
	 * @see #Vector3D(double, double, double)
	 */
	public double getY() {
		return y;
	}

	/**
	 * Get the height of the vector.
	 * 
	 * @return height of the vector
	 * @see #Vector3D(double, double, double)
	 */
	public double getZ() {
		return z;
	}

	/**
	 * Get the norm for the vector.
	 * 
	 * @return euclidian norm for the vector
	 */
	public double getNorm() {
		return Math.sqrt(x * x + y * y + z * z);
	}

	/**
	 * Get the azimuth of the vector.
	 * 
	 * @return azimuth (&alpha;) of the vector, between -&pi; and +&pi;
	 * @see #Vector3D(double, double)
	 */
	public double getAlpha() {
		return Math.atan2(y, x);
	}

	/**
	 * Get the elevation of the vector.
	 * 
	 * @return elevation (&delta;) of the vector, between -&pi;/2 and +&pi;/2
	 * @see #Vector3D(double, double)
	 */
	public double getDelta() {
		return Math.asin(z / getNorm());
	}

	/**
	 * Add a vector to the instance.
	 * 
	 * @param v
	 *            vector to add
	 * @return a new vector
	 */
	public Vector3D add(final Vector3D v) {
		return new Vector3D(x + v.x, y + v.y, z + v.z);
	}

	/**
	 * Add a scaled vector to the instance.
	 * 
	 * @param factor
	 *            scale factor to apply to v before adding it
	 * @param v
	 *            vector to add
	 * @return a new vector
	 */
	public Vector3D add(final double factor, final Vector3D v) {
		return new Vector3D(x + factor * v.x, y + factor * v.y, z + factor * v.z);
	}

	/**
	 * Subtract a vector from the instance.
	 * 
	 * @param v
	 *            vector to subtract
	 * @return a new vector
	 */
	public Vector3D subtract(final Vector3D v) {
		return new Vector3D(x - v.x, y - v.y, z - v.z);
	}

	/**
	 * Subtract a scaled vector from the instance.
	 * 
	 * @param factor
	 *            scale factor to apply to v before subtracting it
	 * @param v
	 *            vector to subtract
	 * @return a new vector
	 */
	public Vector3D subtract(final double factor, final Vector3D v) {
		return new Vector3D(x - factor * v.x, y - factor * v.y, z - factor * v.z);
	}

	/**
	 * Get a normalized vector aligned with the instance.
	 * 
	 * @return a new normalized vector
	 * @exception ArithmeticException
	 *                if the norm is zero
	 */
	public Vector3D normalize() {
		final double s = getNorm();
		if (s == 0) {
			throw new ArithmeticException("cannot normalize a zero norm vector");
		}
		return scalarMultiply(1 / s);
	}

	/**
	 * Get a vector orthogonal to the instance.
	 * <p>
	 * There are an infinite number of normalized vectors orthogonal to the
	 * instance. This method picks up one of them almost arbitrarily. It is
	 * useful when one needs to compute a reference frame with one of the axes
	 * in a predefined direction. The following example shows how to build a
	 * frame having the k axis aligned with the known vector u :
	 * 
	 * <pre>
	 * &lt;code&gt;
	 *   Vector3D k = u.normalize();
	 *   Vector3D i = k.orthogonal();
	 *   Vector3D j = Vector3D.crossProduct(k, i);
	 * &lt;/code&gt;
	 * </pre>
	 * 
	 * </p>
	 * 
	 * @return a new normalized vector orthogonal to the instance
	 * @exception ArithmeticException
	 *                if the norm of the instance is null
	 */
	public Vector3D orthogonal() {

		final double threshold = 0.6 * getNorm();
		if (threshold == 0) {
			throw new ArithmeticException("null norm");
		}

		if ((x >= -threshold) && (x <= threshold)) {
			final double inverse = 1 / Math.sqrt(y * y + z * z);
			return new Vector3D(0, inverse * z, -inverse * y);
		} else if ((y >= -threshold) && (y <= threshold)) {
			final double inverse = 1 / Math.sqrt(x * x + z * z);
			return new Vector3D(-inverse * z, 0, inverse * x);
		}
		final double inverse = 1 / Math.sqrt(x * x + y * y);
		return new Vector3D(inverse * y, -inverse * x, 0);

	}

	/**
	 * Compute the angular separation between two vectors.
	 * <p>
	 * This method computes the angular separation between two vectors using the
	 * dot product for well separated vectors and the cross product for almost
	 * aligned vectors. This allow to have a good accuracy in all cases, even
	 * for vectors very close to each other.
	 * </p>
	 * 
	 * @param v1
	 *            first vector
	 * @param v2
	 *            second vector
	 * @return angular separation between v1 and v2
	 * @exception ArithmeticException
	 *                if either vector has a null norm
	 */
	public static double angle(final Vector3D v1, final Vector3D v2) {

		final double normProduct = v1.getNorm() * v2.getNorm();
		if (normProduct == 0) {
			throw new ArithmeticException("null norm");
		}

		final double dot = dotProduct(v1, v2);
		final double threshold = normProduct * 0.9999;
		if ((dot < -threshold) || (dot > threshold)) {
			// the vectors are almost aligned, compute using the sine
			final Vector3D v3 = crossProduct(v1, v2);
			if (dot >= 0) {
				return Math.asin(v3.getNorm() / normProduct);
			}
			return Math.PI - Math.asin(v3.getNorm() / normProduct);
		}

		// the vectors are sufficiently separated to use the cosine
		return Math.acos(dot / normProduct);

	}

	/**
	 * Get the opposite of the instance.
	 * 
	 * @return a new vector which is opposite to the instance
	 */
	public Vector3D negate() {
		return new Vector3D(-x, -y, -z);
	}

	/**
	 * Multiply the instance by a scalar
	 * 
	 * @param a
	 *            scalar
	 * @return a new vector
	 */
	public Vector3D scalarMultiply(final double a) {
		return new Vector3D(a * x, a * y, a * z);
	}

	/**
	 * Compute the dot-product of two vectors.
	 * 
	 * @param v1
	 *            first vector
	 * @param v2
	 *            second vector
	 * @return the dot product v1.v2
	 */
	public static double dotProduct(final Vector3D v1, final Vector3D v2) {
		return v1.x * v2.x + v1.y * v2.y + v1.z * v2.z;
	}

	/**
	 * Compute the cross-product of two vectors.
	 * 
	 * @param v1
	 *            first vector
	 * @param v2
	 *            second vector
	 * @return the cross product v1 ^ v2 as a new Vector
	 */
	public static Vector3D crossProduct(final Vector3D v1, final Vector3D v2) {
		return new Vector3D(v1.y * v2.z - v1.z * v2.y, v1.z * v2.x - v1.x * v2.z, v1.x
				* v2.y - v1.y * v2.x);
	}

	/** Abscissa. */
	private final double x;

	/** Ordinate. */
	private final double y;

	/** Height. */
	private final double z;

	/** Serializable version identifier */
	private static final long serialVersionUID = -5721105387745193385L;

}
